In the year 1996 Uruguay carried out a constitutional reform that introduced substantial changes in the previous electoral system. From an institutionalism perspective, it could be expected that those changes affected the actors' incentives and strategies. Within this logic, this article inquires into the possible effects that modifications of some electoral rules may produce in the patterns of intraparty cooperation and competition. The aim is to register the change in the incentives of the actors at the local level, in order to cooperate with the actors at the national level in legislative and presidential elections. This analysis is done through a case study: the leaders and local groups from Partido Nacional in the district of Maldonado (1994-2005).